Finite-Time Command Filtered Control of Three-Phase AC/DC Converter Under Unbalanced Grid Conditions
Cheng Fu, Chenghui Zhang, Guanguan Zhang, Chen Zhang, Qijun Su
Abstract
For the three-phase ac/dc converter, unbalanced grid voltages cause grid current distortions and dc-link voltage fluctuations, threatening the safe operation of the power grid or loads. To address this issue, the control targets of the ac/dc converter under unbalanced grids are transformed into a unified power tracking problem by introducing modified power references. Then, the finite-time command filtered control (FTCFC) of the ac/dc converter is proposed, and the dual-loop control structure of inner power and outer dc-link voltage is studied, where the active and reactive powers are independently regulated without the current control loop and the phase-locked loop. In this method, the proposed command filter estimates the power references' derivatives, and the fixed-time disturbance observer is designed to suppress the unknown load disturbances on the dc-link voltage control loop. Theoretical analysis and experimental results validate the effectiveness of the proposed FTCFC method, and the fast and accurate power tracking performance is achieved for all three control modes. Compared with the PI+backstepping control, the FTCFC method improves the tracking performance of the dc-link voltage and powers and reduces the current THD by 35.2%.